2) Afterwards please unzip the package you got from themeforest.net ONE time. You should get a folder which contains PSDs, Docs and another zip file (which is called flashlight.zip. This zip file is the right file. Go to your wordpress admin panel and navigate to Appearance > Themes. Then select the flashlight.zip file, upload & install it. You can also unpack this zip file and upload the resulting folder via ftp to wp-content/themes.

3) Basically yes – you can create the website offline and move it to your main domain afterwards. However this requires some advanced knowledge (sql database restore/backups, sql file editing, database tool usage, ftp usage, etc.) – if you’re not sure how to do this please don’t try it otherwise it’s just frustrating. We can’t assist you when it comes to server maintenance, etc.